Preservative efficacy (preservative challenge) testing

Included in our scope of accreditation under the Campden Laboratory Accreditation Scheme.

Preservative efficacy (challenge) testing provides a means of predicting preservative adequacy under normal conditions of storage and use and constitutes a key element of product safety assessment and shelf life/PAO substantiation.

Donnington Laboratories Ltd offers preservative efficacy testing in accordance with:

  • British and European Pharmacopoeias
  • USP
  • EN ISO 11930
  • client specified protocols (e.g. single/mixed culture approaches and repeat insult tests)
  • in-house protocols for screening, investigative and/or confirmatory purposes

Unless otherwise instructed, it is our policy to apply the BP/EP method with the addition of E coli for topical products. In our view, this offers maximum regulatory acceptability combined with the most reliable prediction of preservative efficacy. However, whether you use the pharmacopoeial tests, EN ISO 11930, your own in house protocol or a combination of various methods, we are committed to providing the best possible service, tailored to suit your individual requirements. We are happy to include supplementary test organisms, on either a single or mixed culture basis, and to retest after a period of accelerated storage to confirm microbial stability over shelf life and PAO in the case of personal care products. Reliably predictive data in the case of aggressive or preservative tolerant strains can be particularly difficult to generate and is an area in which DLL has considerable experience.

Method validation:

Where requested, performed in accordance with EP 2.6.12.


In addition to providing signed master copies of final reports, it is our standard practice to provide interim updates by email after each inspection point. This enables clients to track sample performance and provides early warning of possible shortcomings. Where development schedules are tight an early indication can be essential to achieving deadlines and launch dates.

Discontinuation Policy:

Preservative challenge testing can be discontinued at any stage, if so requested. Under these circumstances, DLL will only charge for work completed up to the point of termination.


Test Turnaround (days) Min sample requirement Price/sample
BP/EP (5 organism)/USP 40 (max) 150g/ml £175
BP/EP (4 organism – topicals) 40 (max) 100g/ml £140
Additional inocula (single or mixed culture) 40 (max) As above + 30g/ml per inoculum As above + £42 per extra inoculum
EN ISO 11930 40 (max) 150g/ml £175
In house (mixed culture) 40 (max) 75g/ml £110
Client specific methods Designated storage period plus 10 days 30g/ml per inoculum PoA
Dilution-neutralisation validation (EP 2.6.13) 3 (bacteria)
5 (yeast/mould)
20g/ml £60 (in combination with challenge) £75 (if conducted alone)
Wipe in pack 40 (max) 6 packs £220.00
  • based on charges for single sample submission. Significant discounts are available for sample submissions comprising multiple samples. Contact us for a quotation.
  • Please ensure that samples are suitably packaged to avoid damage in transit

All prices exclude VAT